1. Field of the Invention
The present invention relates to an ultrasonic sensor having a piezoelectric element connected to an acoustic matching member.
2. Description of Related Art
An ultrasonic sensor having a piezoelectric element mounted on a substrate such as a metallic or resin substrate has been known hitherto. The ultrasonic sensor receives ultrasonic waves transmitted from a transmitter and reflected on an object to be detected. Based on signals outputted from the ultrasonic sensor, a position and/or a distance of the object is detected in a two- or tree-dimensional manner.
Some of the ultrasonic sensors include an acoustic matching layer or a member for adjusting acoustic impedance and for improving a receiving efficiency of ultrasonic waves. An example of the ultrasonic sensor having the acoustic matching layer is disclosed in JP-A-2002-354591. In this example, an acoustic matching layer is connected to a center portion of a surface of the piezoelectric element.
In this type of the ultrasonic sensor, the piezoelectric element is sandwiched by a pair of electrodes, and one of the electrodes is connected to the acoustic matching layer. The electrode of the piezoelectric element connected to the acoustic matching layer is made larger than the acoustic matching layer to connect a lead wire to the electrode of the piezoelectric element.
However, if the electrode area connected to the acoustic matching layer is made larger than that of the acoustic matching layer, there is a portion of the piezoelectric element that is not connected to the acoustic layer. The non-connected portion of the piezoelectric element vibrates in a phase different from that of the connected portion, generating noises or causing attenuation of vibration. This results in decrease in detection efficiency. It is also conceivable to insert a wiring member between the electrode of the piezoelectric element and the acoustic matching layer. In this case, however, the piezoelectric element may be connected to the acoustic matching layer in a slanted manner, or a boundary may be formed between the piezoelectric element and the acoustic matching layer. The slanted connection and/or the boundary may cause attenuation of vibration and decrease in a connecting force between the piezoelectric element and the acoustic matching layer.